A piston within an internal combustion engine must dissipate the heat energy it absorbs, during each engine cycle, from the conversion of chemical energy into heat energy and finally into mechanical work.
Pistons are commonly made from aluminum or iron alloys. A piston typically has a crown portion with an upper surface exposed to engine combustion and the temperatures associated therewith. An undercrown portion of the piston is exposed to crankcase fluids. A ring belt, carrying compression and oil control rings, depends or extends from the crown portion. A piston skirt portion, having generally curved sidewalls, extends from the ring belt portion to provide a reaction force to counter the thrust forces exerted on the piston. A pin boss may extend between the skirt sidewalls for receiving a wrist pin for connection with a connecting rod.
In operation, the piston crown portion absorbs heat energy from an engine combustion chamber. The heat energy absorbed by the crown portion is conducted through the piston to the undercrown portion, the ring belt, and the skirt portion. Heat energy within the ring belt and skirt portion is conducted to the associated engine cylinder bore by direct contact and through the piston rings. The heat energy within the undercrown portion is transferred to the ring belt or dissipated to crankcase fluids, including air, oil vapor, and liquid oil present in the engine. By increasing the amount of liquid oil supplied to the undercrown portion of the piston, the operating temperature of the piston can be reduced, thereby increasing the durability of the piston and enabling increased engine performance.